This invention relates to 6000 series aluminum alloys. More particularly, it relates to 6XXX alloys that are brazeable per a process that employs Nocolok(copyright) brand fluxes (sometimes referred to as the xe2x80x9cNocolok brazing processxe2x80x9d). Nocolok is a registered trademark of Alcan Aluminium Ltd of Canada. Typical 6000 Series or 6XXX brazing alloys include 6063 and 6005 aluminum (Aluminum Association designations). While said alloys may be brazed via the Nocolok process, they generally exhibit poor machinability (C or D ratings). The reason for their brazing success lies in the fact that their Mg contents lie well below 0.5 wt. %. 6XXX alloys with greater than 0.5 weight percent Mg, such as 6061 aluminum, don""t perform as well in Nocolok brazing operations. It is believed their higher Mg levels tend to poison the brazing flux by the formation of Mgxe2x80x94F compounds (like MgF2).
Numerous brazeable aluminum alloys have been patent protected. Representative compositions include those taught by U.S. Pat. Nos. 4,040,822, 5,375,760, 5,520,321, 5,535,939, and 5,564,619. Still other aluminum alloys, not specific to brazing, with Nocolok or otherwise, are taught in U.S Pat. Nos. 2,096,010, 4,589,932, 5,286,445, 5,522,950 and 5,587,029.
A 6XXX alloy that is Nocolok(copyright) brazeable and has B-rated machineability or better was created using a base composition with slightly less than 0.5 wt. % Mg, but excess Si for strengthening. Tin (Sn) was added thereto to enhance the overall machineability of products made from this alloy. Sn has a relatively low melting point. But when Sn is present in large amounts, the alloy may flow unacceptably during brazing. A primary objective of this invention is to create a Nocolok(copyright) brazeable 6XXX alloy that balances Sn levels to be just high enough for B-machinability or better without causing the aforesaid flow problems. Another primary objective is to add sufficient amounts of magnesium to this alloy for strength, but still maintain good brazeability.
All component percentages herein are by weight percent unless otherwise indicated. Also, when referring to any numerical range of values, such ranges are understood to include each and every number and/or fraction between the stated range mininum and maximum. A range of about 0.5 to 1.2 wt % silicon, for example, would expressly include all intermediate values of about 0.6, 0.7 and 0.8% Si, all the way up to and including 1.1 and 1.19% Si. The same applies to each other numerical property and/or elemental range set forth herein.
In a broad sense, the brazeable aluminum alloy of this invention comprises an alloy consisting essentially of about 0.5-1.2 wt. % Si; up to about 0.5 wt. % Fe; up to about 0.3 wt. % Cu; between about 0.4-0.6 wt. % Mg; up to about 0.35 wt. % Mn; up to about 0.15 wt. % Cr; between about 0.4-0.8 wt. % Sn; up to about 0.2 wt. % Zn, the balance aluminum, incidental elements and impurities. On a less preferred basis, Bi, In, Cd or combinations thereof, may be substituted for some of the Sn therein. And while preferred embodiments of this invention are best suited for brazing-type applications, it is to be understood that the same alloy may have suitable non-brazing end uses as well.
On a more preferred basis, the alloy composition of this invention consists essentially of: about 0.6-0.8 wt. % silicon; about 0.2-0.4 wt. % iron; about 0.05-0.15 wt. % copper; about 0.4-0.5 wt. % magnesium; up to about 0.35 wt. % Mn; up to about 0.15 wt. % chromium; between about 0.5-0.6 wt. % tin; up to about 0.1 wt. % titanium; up to about 0.20 wt. % zinc, the balance aluminum, incidental elements and impurities. This product is preferentially processed into one or more of the following tempers: T1, T5, T6, T651, T6510, T6511, T8, T851, and T9.